Method and apparatus for continuous casting



April 8, 1969 METHOD AND POPP ATUS F ONTINUOUS CASTING Filed Sept 8, 1965 In van/or 611 /25! 5 fa N :1: n. B); W M

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United States Patent US. Cl. 164-82 13 Claims ABSTRACT OF THE DISCLOSURE A continuous casting mold provided with a series of normally open expansion grooves on the inner mold surfaces to accommodate temperature gradient stresses in the mold. Furthermore, the melt surface level is kept between the upper and lower limits of said expansion grooves.

Molds for continuous casting are generally made from pure copper of from metals and alloys having a higher strength and lower heat conductivity than copper. The mold consists either of a tubular mold, a plate mold or block mold. A tubular mold consists of a seamless tube. A plate mold is assembled from a plurality of plates. A block mold consists of a cast or forged block. In any case, the manufacture of the molds for continuous casting involves substantial costs so that the durability of the molds is significant for the economy of the continuous casting process.

The molds are subject to certain typical changes in operation. These changes necessitate eventually a remachining or scrapping of the molds. The thin-walled tubular molds become mainly unsuitable for further use because the mold wall bulges inwardly into the mold cavity adjacent to the level of the melt surface so that the mold cavity is constricted. Plate molds and block molds become mainly unsuitable for further use due to warping and fire cracks. Longitudinal cracks have also been observed, mainly in molds made from a high-strength material.

It has already been recognized that these defects are due to the high temperature difference between the inside surface of the mold wall, which surface is contacted by the molten material, and the water-cooled outside surface of the mold wall. The high temperature differences in the mold wall and the temperature fluctuations which occur mainly on the level of the melt surface result in high stresses and permanent deformation in the mold wall.

For this reason it has already been suggested to reduce the stresses occurring in the mold wall and the deforming action of such stresses by providing expansion grooves in the mold wall on the outside surface thereof. The resulting improvement in the durability of the molds, however, is not satisfactory.

The present invention is based on the recognition that the inside surface of the mold wall, which surface defines the mold cavity, is subjected to higher temperature fluctuations than the cooled outside surface and that it is preferable for this reason to provide normally open expansion grooves in the inside surfaces of the mold wall, which inside surfaces define the mold cavity. As a result, the dissipation of the stresses is much improved thereby compensating for the differential expansions.

It has been found that with most kinds of steel and the usual casting temperatures, the width of the expansion grooves may be as large as 0.8 mm. The expansion grooves are preferably formed with the aid of milling cutters, which may be used for providing expansion grooves as small as 0.2 mm. in width.

It has also been found that warpage of the mold Wall, constriction of the mold cavity at the level of the melt surface and formation of longitudinal cracks in the mold wall are preferably overcome by vertical expansion grooves, and that is is sufficient to provide such grooves adjacent to the level of the melt surface.

In view of the general strength of the mold it is further proposed that the expansion grooves should begin 1050 mm. below the top edge of the mold and should extend below the level of the melt surface. In thin-walled molds, the depth of the expansion grooves should be about one half of the wall thickness. In thick-walled molds, the depth of the expansion grooves should be at least 4 mm.

The expansion grooves are preferably evenly spaced around the periphery of the mold, for instance, with a spacing of about 5 mm. between the grooves. Good results may also be achieved with grooves having a greater spacing. Even grooves spaced about 50 mm. apart have a satisfactory effect in opposing the formation of longitudinal cracks in a mold wall consisting of relatively brittle material. Although the stresses having a peripheral direction predominate, particularly adjacent to the level of the melt surface, substantial stresses which are directed longitudinally of the mold are also present. For this reason the provision of horizontal expansion grooves according to the invention is also proposed. They improve the protection against a premature formation of fire cracks.

A portion of the top part of a mold according to the invention is shown by way of example on the accompanying drawing, in which FIG. 1 is a fragmentary transverse sectional view; and

FIG. 2 is a fragmentary longitudinal sectional view.

With reference to FIGS. 1 and 2, normally open expansion grooves 1 extend at right angles and have been machined by means of milling cutters in the inside surfaces 3 of mold Wall 2.

The invention is not to be confined to any strict conformity to the showings in the drawings but changes or modifications may be made therein so long as such changes or modifications mark no material departure from the spirit and scope of the appended claims.

What is claimed is:

1. A continuous casting mold comprising mold walls having inside surfaces defining a mold cavity and a series of expansion grooves formed in said inside surfaces to accommodate temperature gradient stresses therein.

2. A mold as set forth in claim 1, in which said expansion grooves have a width of 0.2 to 0.8 mm.

3. A mold as set forth in claim 1, in which said expansion grooves extend vertically.

4. A mold as set forth in claim 1, which has a length confining a melt surface level and said expansion grooves are formed adjacent to said level.

5. A mold as set forth in claim 4, in which said mold has a portion of its length free of expansion grooves.

6. A mold as set forth in claim 5, in which said mold has a top rim, said expansion grooves having top ends spaced 10-50 mm. below said top rim, said melt surface level being between top ends and bottom ends of said grooves.

7. A mold as set forth in claim 1, in which the depth of said expansion grooves is about one half of the thickness of said mold walls.

8. A mold as set forth in claim 1, in which the depth of said expansion grooves is at least 4 mm.

9. A mold as set forth in claim 1, in which said expansion grooves are uniformly spaced around the inside periphery of said mold.

10. A mold as set forth in claim 1, in which said expansion grooves are spaced 5 mm. to 50 mm. apart.

11. A mold as set forth in claim 1, which has a length confining a melt surface level and in which part of said expansion grooves extend vertically and part of said expansion grooves extend substantially horizontally and adjacent to said melt surface level.

12. A process of continuous casting in a tubular mold which comprises inside surfaces defining a mold cavity and formed with expansion grooves, which process comprises maintaining in said mold cavity a melt surface at a level adjacent to said expansion grooves.

13. A process of continuous casting in a tubular mold which comprises inside surfaces defining a mold cavity and formed with vertical expansion grooves and with substantially horizontal expansion grooves, which process comprises maintaining in said mold cavity a melt surface at a level adjacent to said substantially horizontal expansion grooves.

References Cited UNITED STATES PATENTS,

288,969 11/1883 Barr 164-373 Re. 10,804 2/1887 Whitney 249-79 481,442 8/1892 Treat 164373 528,034 10/1894 Schon 249-49 532,888 1/1895 Matheus 249-79 3,203,055 8/1965 Bungeroth et al 164-280 3,336,973 8/1967 Ratclifie 164-283 FOREIGN PATENTS 985,119 3/1951 France.

I. SPENCER OVERHOLSER, Primary Examiner.

R. SPENCER, ANNEAR, Assistant Examiner.

U.S. Cl. X.R. 164-273 

